Cash-strapped Nigeria turns to oil swaps to stave off gasoline shortages
* Oil slump left Nigeria short of funds to import oil products * NNPC has ramped up deals to exchange oil for oil products * Contracts not yet signed, vulnerable to changes at NNPC By Libby George and Julia Payne LONDON/ABUJA, March 17 (Reuters) - Nigeria is set to ramp up the amount of crude oil it swaps for vital gasoline imports by more than a third as it grapples with the worst economic crisis in years and upheaval in its graft-ridden energy sector. A more than 60 percen